PLAN B
One should always have an approach to considering a broad differential in a case that you do not immediately recognize (PLAN A) One popular pneumonic is:
VIINNDDICATE
Normal/variant
Physics/artifact
Vascular
Infection/Inflammatory
Neoplasm, benign, malignant
Drugs/toxic
Degenerative
Iatrogenic
Congenital/developmental
Autoimmune/allergic
Trauma
Endocrine/metabolic